- Your company makes hollow ping pong balls and you need to calibrate the machine that produces them. The volume of material used in each ball is given by V = n(r3r3), where r, is the outer radius and r is the inner radius. Your ping pong ball machine produces balls with an outer radius of ro = 40 mm 0.1 mm. The company is targeting a volume uncertainty of 13575 mm. What inner radius uncertainty is required if the nominal inner radius is r= 39.6 mm?